Issue 52

J. Kasivitamnuay et alii, Frattura ed Integrità Strutturale, 52 (2020) 163-180; DOI: 10.3221/IGF-ESIS.52.14

Specifications The software specifications are related to the types and levels of assessments, cracked component geometries, and types of applied loads. The software was specified to perform integrity, leak-before-break (LBB), and remaining life assessments of a cracked cylinder. Four types of cracked cylinder (namely CTCL, CTCC, CSCLE, and CSCCE) were considered, as illustrated in Fig. 5. For CSCLE and CSCCE, both the inner-wall and outer-wall cracks were included in the study. The treatments of crack interaction and weld strength mismatch were not included. The SI unit system was adopted. The integrity assessment covered levels 1, 2, and 3 option B. The LBB assessment was permitted for the level 2 and 3 assessments, whereas the remaining life assessment permitted only a level 3 assessment. For the LBB assessment, the user must provide the length of a through-wall crack at a detectable leak rate. The remaining life assessment covered only the crack growth mechanism by fatigue. Furthermore, only cyclically nominal loads with a constant amplitude were considered. The analysis was performed at two representative locations on the crack front. The applied loads on the cylinder could be nominal loads, i.e. internal pressure, axial force, and bending moment, as well as through-thickness mechanical, thermal, and residual stress distribution perpendicular to the crack plane. These stress profiles are expressed in the form of Eqn. (3), where the coefficients in the equation are specified for given types and directions of stresses. The coefficients of thermal stress profiles were provided by the user. Meanwhile, for residual stress, the user has a choice of whether to use the recommended profiles in the standard.

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Figure 5: Types of cracked cylinder included in the software: (a) CTCL; (b) CTCC; (c) CSCLE (inner-wall crack); (d) CSCLE (outer wall crack); (e) CSCCE (inner-wall crack); and (f) CSCCE (outer-wall crack).

The software incorporated a text file containing a material information of some pressure vessel steels. The information includes material specifications, specified minimum yield strength (SMYS), and specified minimum ultimate strength (SMTS). However, the software allowed the user to input actual material information. The constitutive equation incorporated in the software was only the Ramberg-Osgood (R-O) model. The parameters of the R-O model can be user defined input or estimated by the formulas in the standard. The fracture toughness could be the custom input value or estimation from various methodologies in Tab. 1. The supported fatigue crack growth rate (FCGR) models were Paris and Walker models, with the material parameters being user provided.

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